Abstract: A power system includes a power source, field gas supply, and natural gas supply, and is operable using a gas mixture comprising field gas from the field gas supply and natural gas from the natural gas supply. A ratio of field gas to natural gas is adjusted based on sensed property of the field and/or natural gas, change in a condition of the field and/or natural gas, measured emissions from the power source, predicted emissions from the power source, and/or direct/indirect feedback from the power source. A method for operating a power system includes: connecting a mixing gas line and a field gas line to a power source at work site; determining a ratio of mixing gas to field gas; combining mixing gas from the mixing gas line and field gas from the field gas line based on the determined ratio; and operating the power source with the combined gases.